Melanosis of oral and genital mucosae (labial lentigo, lentiginosis of oral mucosa, genital lentiginosis) are benign melanotic macules characterized by single or often numerous lesions with a tendency to confluence. 
Despite its benign behavior, the clinical aspect of melanosis on each of the above mentioned anatomic sites (oral mucosa; lower lip; vulva and penis) may frequently share features with melanoma in situ. In all these instances a punch biopsy with subsequent histopathologic examination is crucial in order to rule out melanoma in situ. Although melanotic macules are regarded by most authors as wholly benign lesions mimicking melanoma in situ only from a clinical standpoint, some authors also consider these melanotic macules as precursor lesions of melanoma [Barnhill et al. 1990]. At present, results of prospective, large-scale studies focusing on patients with genital and oral lentiginosis are not available to predict the natural history of genital and oral lentiginosis or its relation to mucocutaneous melanoma.

Clinical features

Clinically, labial lentigo is usually situated on the lower lip and appears as a roundish, well circumscribed, light-brown macule. In contrast to the solitary labial lentigo, melanosis of the male and female genitalia is characterized by numerous, multifocal, relatively large (up to 2 cm), irregularly outlined macules with a variegated brownish pigmentation displaying a speckled pattern. Commonly they were regarded as having an atypical clinical appearance and at least close clinical follow-up examinations or, even better, punch biopsies are recommended.

Dermoscopic features

A practical problem, especially when examining melanosis of the vulva and the penis, is the close working distance when using the conventional dermatoscope. Nevertheless, the dermoscopic features of melanosis on both oral and genital locations are rather characteristic, revealing diffuse pigmentation with a peculiar parallel pattern of partially linear and partially curvilinear light-brown to dark-brown streaks. Furthermore, based on our experience, melanoma-specific criteria such as atypical pigment network variations, irregular dots/globules and blue-whitish veil have not been found in benign labial and genital melanosis.